1. Field of the Invention
This invention relates to a precise adjustment drive apparatus, particularly an apparatus for finely adjusting postures of optical elements (lens, mirror, etc.) of an exposure apparatus for use in steps of producing a semiconductor or liquid crystal device. More specifically, the posture adjustment is performed for obtaining a more correct relation of image formation when an image of an original plate (e.g. mask or reticle) is projected and exposed on an object (e.g. wafer) with optical elements.
2. Related Background Art
A semiconductor exposure apparatus is an apparatus transferring an original plate (e.g. reticle) having a large number of different types of patterns to a silicon wafer (substrate). For fabricating a circuit having a high integration degree, it is essential to improve not only a resolution performance but also superimposition accuracy.
Superimposition errors in the semiconductor exposure apparatus are classified into an alignment error, image deformation and a magnification error. The alignment error can be alleviated by adjustment of a relative position between the original plate (reticle) and the substrate (wafer). On the other hand, the image deformation and the magnification error can be adjusted by moving some of optical elements of an optical system. If some optical elements are moved in a direction other than a desired direction of movement, or the optical element is decentered or inclined when some optical elements are moved, a desired optical performance (optical performance with image deformation and the magnification error corrected) cannot be obtained. For example, if it is necessary to move the optical element along the optical axis, parallel decentering and inclination decentering error components should be prevented from growing.
As an optical element movement apparatus for semiconductor exposure apparatus, an apparatus with a mechanism using a parallel plate has been devised (Japanese Patent Application Laid-Open No. 2000-357651). FIGS. 15A and 15B are a top view and a sectional view, respectively, of the conventional optical element moving apparatus.
As shown in these figures, in the conventional optical element moving apparatus, a ring-like flat spring 11 having a moving table 1 holding an adjustment lens 7 for adjusting a magnification, an aberration and the like of an optical system and a cell 8 supporting the adjustment lens 7, and a fixed table 2 is fixed on both end faces of the moving table 1 and the fixed table 2 in a sealed manner. The moving table 1 has a cylindrical shape, but the outer diameter of the upper face is unequal to the outer diameter of the lower face. Furthermore, similarly, the fixed table 2 also has a cylindrical shape, the inner diameter of the opening of the upper face is unequal to the inner diameter of the opening of the lower face. The fixed table 2 has at least one hole, and can change the position of a moving part by a change in pressure or volume of a driving fluid.
Other examples of the conventional technique include an optical element micro adjustment apparatus described in U.S. Pat. No. 5,986,827, but in the structure thereof, adjustment is limited to micro adjustment of three axes, and adjustment within the optical element surface cannot be performed, and therefore the apparatus is not sufficient for applications precise adjustment of positions and postures of optical elements.
Furthermore, another example of the conventional technique is an apparatus described in Japanese Patent Application Laid-Open No. 2002-131605, but it utilizes a contraction mechanism using a long lever (long distance between support point and power point or action point), and is therefore expected to have a low specific frequency. The low specific frequency is disadvantageous for applications requiring precise adjustment of positions and postures because vibrations from outside the apparatus are transferred to a moving part. Furthermore, the low specific frequency is disadvantageous when high-speed drive is required.
In Japanese Patent Application Laid-Open No. 2000-357651, other parallel decentering and inclination decentering components associated with optical elements depend on guidance accuracy of a flat spring guide. Furthermore, the initial position and posture of the optical element depend on assembly accuracy of apparatus. However, as semiconductor device patterns have become more precise, higher position and posture accuracy than ever and drive positioning accuracy for correction of aberrations and the like have been required for the optical element. Thus, the apparatus driving only one axis or three axes, described in Japanese Patent Application 2000-357651 or U.S. Pat. No. 5,986,827 is not sufficient, and an apparatus capable of adjusting total six axes of orthogonal three axes in the translational direction and three axes about the translational axes is desired.
Furthermore, for alleviating a positional shift of the optical element due to vibrations from outside the apparatus, a six-axis adjusting mechanism provided therein a mechanism for preventing transfer of external vibrations to the optical element is desired.
Further, in recent years, as semiconductor patterns have become more precise, an exposure apparatus using light having a short wavelength (e.g. light having a wavelength of 10 to 15 nm, such as EUV light) has been devised. For obtaining a relation of image formation required for the exposure apparatus using EUV light, higher position and posture accuracy than ever and drive positioning accuracy for correction of aberrations and the like have been required for the optical element. However, if means for measuring a position from a basic structure can measure only a relative displacement with a moving part, a positioning sensor for positioning the moving part with respect to a reference (e.g. fixed part) is required. If the moving part is positioned with respect to the fixed part based on the result of detection by the positioning sensor, an imposition error of the fixed part and a measurement error of the positioning sensor appear as a positioning error of the moving part.
Alternatively, for obtaining the required relation of image information, an apparatus capable of controlling a relative position between moving parts including different optical elements.
Furthermore, the optical element is expected to have an elevated temperature due to exposure heat to cause thermal distortion. If the optical element is thermally distorted, the exposure apparatus no longer satisfies the required relation of image formation, and therefore it is necessary to cool the optical element. Particularly, positioning accuracy in the order of nanometers is required for the optical element of the EUV exposure apparatus, and therefore cooling means transferring no vibrations to the optical element should be used.
Furthermore, since EUV light is easily absorbed by a material, the amount of light decreases if a contamination (hydrocarbon compound generated from the wafer) occurs. Further, there arises a problem such that EUV light reacts with the contamination to deposit carbon and the like on the surface of the optical element, thus reducing a reflectivity of the optical element. Thus, the partial pressure of contamination in a body tube space through which EUV light passes should be kept at a low level.
Thus, the exemplary object of the present invention is to provide a positioning apparatus capable of performing positioning control of optical elements in directions of six axes with high accuracy, and an exposure apparatus.